Unit 2 Virtualization Part I.pptx

Introduction:
• Virtualization is a large umbrella of technologies and concepts
that are meant to provide an abstract environment whether
virtual hardware or an operating system to run applications.
• Virtualization Technology is one of the fundamental
components of cloud computing, especially in regard to
Infrastructure-based services.
• Virtualization allows the creation of a secure, customizable,
and isolated execution environment for running applications.
• These environments are called virtual because they simulates
the interface that is expected by a guest.
• Ex:- Hardware Virtualization, Storage & Network
Virtualization.
• Virtualization is widely used to deliver customizable
computing environments on demand.

Major causes for the diffusion of hardware virtualization
solutions are:
a) Increased Performance and Computing Capacity
b) Underutilized hardware and software resources
c) Lack of space
d) Greening initiatives
e) Rise of administrative costs

In a Virtualized Environment, there are three major
components:
1. Guest: The Guest represents the system component
that interacts with the virtualization layer rather than
with the host.
2. Virtualization Layer: The virtualization Layer is
responsible for recreating the same or a different
environment where the guest will operate
3. Host: The Host represents the original environment
where the guest is supposed to be managed.

The Virtualization Reference Model

Characteristics of Virtualized Environments:
1. Increased Security
2. Managed Execution

Characteristics of Virtualized Environments:
2. Managed Execution
a) Sharing
b) Aggregation
c) Emulation
d) Isolation
3. Portability

TAXONOMY OF VIRTUALIZATION TECHNIQUES:
• A classification of Virtualization Techniques helps in
understanding the characteristics and use of these techniques:

• The first classification discriminates against the service or entity that is
being emulated. Virtualization is mainly used to emulate execution
environments, storage, and networks.
• Among these categories, execution virtualization constitutes the oldest,
most popular, and most developed area.
• In particular we can divide these execution virtualization techniques into
two major categories by considering the type of host they require.
I. Process-level techniques are implemented on top of an existing operating
system, which has full control of the hardware.
II. System-level techniques are implemented directly on hardware and do not
require or require a minimum of support from an existing operating
system.
• Within these two categories we can list various techniques that offer the
guest a different type of virtual computation environment: bare hardware,
operating system resources, low-level programming language, and
application libraries.

1. Execution Virtualization
I. Machine Reference Model
II. Hardware-Level Virtualization
III. Hardware Virtualization Techniques
IV. Operating System Level Virtualization
V. Programming Language Level Virtualization
VI. Application Level Virtualization

I. Machine Reference Model

Hypervisors:
• A fundamental element of hardware virtualization is the hypervisor, or virtual machine
manager (VMM). It recreates a hardware environment in which guest operating systems
are installed.
• There are two major types of hypervisor: Type I and Type II (see Figure 3.7).
• Type I hypervisors run directly on top of the hardware. Therefore, they take the place of
the operating systems and interact directly with the ISA interface exposed by the
underlying hardware, and they emulate this interface in order to allow the management
of guest operating systems. This type of hypervisor is also called a native virtual machine
since it runs natively on hardware.
• Type II hypervisors require the support of an operating system to provide virtualization
services. This means that they are programs managed by the operating system, which
interact with it through the ABI and emulate the ISA of virtual hardware for guest
operating systems. This type of hypervisor is also called a hosted virtual machine since it
is hosted within an operating system.

Hypervisors:

Hypervisors:
• Conceptually, a virtual machine manager is internally organized as described in Figure
3.8.
• Three main modules, dispatcher, allocator, and interpreter, coordinate their activity in
order to emulate the underlying hardware.
• The dispatcher constitutes the entry point of the monitor and reroutes the instructions
issued by the virtual machine instance to one of the two other modules.
• The allocator is responsible for deciding the system resources to be provided to the VM:
whenever a virtual machine tries to execute an instruction that results in changing the
machine resources associated with that VM, the allocator is invoked by the dispatcher.
• The interpreter module consists of interpreter routines. These are executed whenever a
virtual machine executes a privileged instruction: a trap is triggered and the
corresponding routine is executed.
• The design and architecture of a virtual machine manager, together with the underlying
hardware design of the host machine, determine the full realization of hardware
virtualization, where a guest operating system can be transparently executed on top of a
VMM as though it were run on the underlying hardware.

Hypervisors:
• Three properties have to be satisfied:
• Equivalence: A guest running under the control of a virtual machine manager
should exhibit the same behavior as when it is executed directly on the physical
host
• Resource control: The virtual machine manager should be in complete control
of virtualized resources.
• Efficiency: A statistically dominant fraction of the machine instructions should
be executed without intervention from the virtual machine manager.
• The major factor that determines whether these properties are satisfied is
represented by the layout of the ISA of the host running a virtual machine
manager.

Hypervisors:
• Popek and Goldberg provided a classification of the instruction set and
proposed three theorems that define the properties that hardware instructions
need to satisfy in order to efficiently support virtualization.
• THEOREM 1: For any conventional third-generation computer, a VMM may
be constructed if the set of sensitive instructions for that computer is a subset
of the set of privileged instructions.
• THEOREM 2: A conventional third-generation computer is recursively
virtualizable if:
 It is virtualizable, and
 A VMM without any timing dependencies can be constructed for it.
• THEOREM 3: A hybrid VMM may be constructed for any conventional
third-generation machine in which the set of user-sensitive instructions is a
subset of the set of privileged instructions

a) Hardware –assisted Virtualization
b) Full Virtualization
c) Paravirtualization
d) Partial Virtualization

a) Hardware –assisted Virtualization:
• This term refers to a scenario in which the hardware provides architectural support for
building a virtual machine manager able to run a guest operating system in complete isolation.
• This technique was originally introduced in the IBM System/370. At present, examples of
hardware-assisted virtualization are the extensions to the x86-64 bit architecture introduced
with Intel VT (formerly known as Vanderpool) and AMD V (formerly known as Pacifica).
• These extensions, which differ between the two vendors, are meant to reduce the performance
penalties experienced by emulating x86 hardware with hypervisors.
• Before the introduction of hardware-assisted virtualization, software emulation of x86
hardware was significantly costly from the performance point of view. The reason for this is
that by design the x86 architecture did not meet the formal requirements introduced by Popek
and Goldberg, and early products were using binary translation to trap some sensitive
instructions and provide an emulated version.
• Products such as VMware Virtual Platform, introduced in 1999 by VMware, which pioneered
the field of x86 virtualization, were based on this technique.
• After 2006, Intel and AMD introduced processor extensions, and a wide range of virtualization
solutions took advantage of them: Kernel-based Virtual Machine (KVM), VirtualBox, Xen,
VMware, Hyper-V, Sun xVM, Parallels, and others.

b) Full Virtualization:
• Full virtualization refers to the ability to run a program, most likely an operating system,
directly on top of a virtual machine and without any modification, as though it were run on the
raw hardware.
• To make this possible, virtual machine managers are required to provide a complete emulation
of the entire underlying hardware.
• The principal advantage of full virtualization is complete isolation, which leads to enhanced
security, ease of emulation of different architectures, and coexistence of different systems on
the same platform.
• Whereas it is a desired goal for many virtualization solutions, full virtualization poses
important concerns related to performance and technical implementation.
• A key challenge is the interception of privileged instructions such as I/O instructions: Since
they change the state of the resources exposed by the host, they have to be contained within the
virtual machine manager. A simple solution to achieve full virtualization is to provide a virtual
environment for all the instructions, thus posing some limits on performance.
• A successful and efficient implementation of full virtualization is obtained with a combination
of hardware and software, not allowing potentially harmful instructions to be executed directly
on the host. This is what is accomplished through hardware-assisted virtualization.

c) Paravirtualization:
• This is a not-transparent virtualization solution that allows implementing thin virtual machine
managers.
• Paravirtualization techniques expose a software interface to the virtual machine that is slightly
modified from the host and, as a consequence, guests need to be modified.
• The aim of paravirtualization is to provide the capability to demand the execution of
performance critical operations directly on the host, thus preventing performance losses that
would otherwise be experienced in managed execution.
• This allows a simpler implementation of virtual machine managers that have to simply
transfer the execution of these operations, which were hard to virtualize, directly to the host.
• To take advantage of such an opportunity, guest operating systems need to be modified and
explicitly ported by remapping the performance-critical operations through the virtual
machine software interface.
• This is possible when the source code of the operating system is available, and this is the reason
that paravirtualization was mostly explored in the opensource and academic environment.
• Whereas this technique was initially applied in the IBM VM operating system families, the
term paravirtualization was introduced in literature in the Denali project [24] at the
University of Washington.

c) Paravirtualization:
• This technique has been successfully used by Xen for providing virtualization solutions
for Linux-based operating systems specifically ported to run on Xen hypervisors.
• Operating systems that cannot be ported can still take advantage of paravirtualization
by using ad hoc device drivers that remap the execution of critical instructions to the
paravirtualization APIs exposed by the hypervisor.
• Xen provides this solution for running Windows-based operating systems on x86
architectures.
• Other solutions using paravirtualization include VMWare, Parallels, and some solutions
for embedded and real-time environments such as TRANGO, Wind River, and XtratuM.

d) Partial Virtualization:
• Partial virtualization provides a partial emulation of the underlying hardware, thus not
allowing the complete execution of the guest operating system in complete isolation.
• Partial virtualization allows many applications to run transparently, but not all the
features of the operating system can be supported, as happens with full virtualization.
• An example of partial virtualization is address space virtualization used in time-sharing
systems; this allows multiple applications and users to run concurrently in a separate
memory space, but they still share the same hardware resources (disk, processor, and
network).
• Historically, partial virtualization has been an important milestone for achieving full
virtualization, and it was implemented on the experimental IBM M44/44X.
• Address space virtualization is a common feature of contemporary operating systems.

IV. Operating System Level Virtualization:
• Operating system-level virtualization offers the opportunity to create different and
separated execution environments for applications that are managed concurrently.
• Differently from hardware virtualization, there is no virtual machine manager or
hypervisor, and the virtualization is done within a single operating system, where the OS
kernel allows for multiple isolated user space instances.
• The kernel is also responsible for sharing the system resources among instances and for
limiting the impact of instances on each other.
• A user space instance in general contains a proper view of the file system, which is
completely isolated, and separate IP addresses, software configurations, and access to
devices.
• Operating systems supporting this type of virtualization are general-purpose,
timeshared operating systems with the capability to provide stronger namespace and
resource isolation.
• Compared to hardware virtualization, this strategy imposes little or no overhead
because applications directly use OS system calls and there is no need for emulation.
• There is no need to modify applications to run them, nor to modify any specific
hardware, as in the case of hardware-assisted virtualization.

IV. Operating System Level Virtualization:
• On the other hand, operating system-level virtualization does not expose the same
flexibility of hardware virtualization, since all the user space instances must share the
same operating system.
• This technique is an efficient solution for server consolidation scenarios in which
multiple application servers share the same technology: operating system, application
server framework, and other components.
• When different servers are aggregated into one physical server, each server is run in a
different user space, completely isolated from the others.
• Examples of operating system-level virtualizations are FreeBSD Jails, IBM Logical
Partition (LPAR), SolarisZones and Containers, Parallels Virtuozzo Containers,
OpenVZ, iCore Virtual Accounts, Free Virtual Private Server (FreeVPS), and others.
• The services offered by these technologies differ, and most of them are available on
Unix-based systems. Some of them, such as Solaris and OpenVZ, allow for different
versions of the same operating system to operate concurrently.

V. Programming-Language-Level Virtualization:
• Programming language-level virtualization is mostly used to achieve ease of deployment
of applications, managed execution, and portability across different platforms and
operating systems.
• It consists of a virtual machine executing the byte code of a program, which is the result
of the compilation process.
• Compilers implemented and used this technology to produce a binary format
representing the machine code for an abstract architecture.
• Generally, these virtual machines constitute a simplification of the underlying hardware
instruction set and provide some high-level instructions that map some of the features of
the languages compiled for them.
• At runtime, the byte code can be either interpreted or compiled on the fly—or jitted—
against the underlying hardware instruction set.
• Programming language-level virtualization has a long trail in computer science history
and originally was used in 1966 for the implementation of Basic Combined
Programming Language (BCPL), a language for writing compilers and one of the
ancestors of the C programming language.
• Other important examples of the use of this technology have been the UCSD Pascal and
Smalltalk.

V. Programming-Language-Level Virtualization:
• Virtual machine programming languages become popular again with Sun’s introduction of the
Java platform in 1996.
• The Java virtual machine was originally designed for the execution of programs written in the
Java language, but other languages such as Python, Pascal, Groovy, and Ruby were made
available.
• The ability to support multiple programming languages has been one of the key elements of
the Common Language Infrastructure (CLI), which is the specification behind .NET
Framework.
• Currently, the Java platform and .NET Framework represent the most popular technologies
for enterprise application development.
• The main advantage of programming-level virtual machines, also called process virtual
machines, is the ability to provide a uniform execution environment across different platforms.
• Programs compiled into byte code can be executed on any operating system and platform for
which a virtual machine able to execute that code has been provided.
• Security is another advantage of managed programming languages; by filtering the I/O
operations, the process virtual machine can easily support sandboxing of applications. As an
example, both Java and .NET provide an infrastructure for pluggable security policies and
code access security frameworks.
• Implementations of this model are also called high-level virtual machines, since high-level
programming languages are compiled to a conceptual ISA, which is further interpreted or
dynamically translated against the specific instruction of the hosting platform.

VI. Application-Level Virtualization:
• Application-level virtualization is a technique allowing applications to be run in runtime
environments that do not natively support all the features required by such applications.
• In this scenario, applications are not installed in the expected runtime environment but are
run as though they were. In general, these techniques are mostly concerned with partial file
systems, libraries, and operating system component emulation.
• Such emulation is performed by a thin layer—a program or an operating system component—
that is in charge of executing the application.
• Emulation can also be used to execute program binaries compiled for different hardware
architectures.
• In this case, one of the following strategies can be implemented: •
 Interpretation: In this technique every source instruction is interpreted by an emulator for
executing native ISA instructions, leading to poor performance. Interpretation has a minimal
startup cost but a huge overhead, since each instruction is emulated.
 Binary translation: In this technique every source instruction is converted to native
instructions with equivalent functions. After a block of instructions is translated, it is cached
and reused. Binary translation has a large initial overhead cost, but over time it is subject to
better performance, since previously translated instruction blocks are directly executed.

VI. Application-Level Virtualization:
• Emulation, as described, is different from hardware-level virtualization. The former simply
allows the execution of a program compiled against a different hardware, whereas the latter
emulates a complete hardware environment where an entire operating system can be installed.
• Application virtualization is a good solution in the case of missing libraries in the host
operating system; in this case a replacement library can be linked with the application, or
library calls can be remapped to existing functions available in the host system.
• Another advantage is that in this case the virtual machine manager is much lighter since it
provides a partial emulation of the runtime environment compared to hardware virtualization.
• Compared to programming-level virtualization, which works across all the applications
developed for that virtual machine, application-level virtualization works for a specific
environment: It supports all the applications that run on top of a specific environment.
• One of the most popular solutions implementing application virtualization is Wine, which is a
software application allowing Unix-like operating systems to execute programs written for the
Microsoft Windows platform.
• Wine features a software application acting as a container for the guest application and a set of
libraries, called Winelib, that developers can use to compile applications to be ported on Unix
systems.
• Wine takes its inspiration from a similar product from Sun, Windows Application Binary
Interface (WABI), which implements the Win 16 API specifications on Solaris.

2. Other Types of Virtualization
I. Storage Virtualization
II. Network Virtualization
III. Desktop Virtualization
IV. Application-Server Virtualization

Virtualization And Cloud Computing:
• Virtualization plays an important role in cloud computing since it allows for the appropriate degree
of customization, security, isolation, and manageability that are fundamental for delivering IT
services on demand.
• Virtualization technologies are primarily used to offer configurable computing environments and
storage. Network virtualization is less popular and, in most cases, is a complementary feature, which
is naturally needed in build virtual computing systems.
• Particularly important is the role of virtual computing environment and execution virtualization
techniques.
• Among these, hardware and programming language virtualization are the techniques adopted in
cloud computing systems. Hardware virtualization is an enabling factor for solutions in the
Infrastructure-as-a-Service (IaaS) market segment, while programming language virtualization is a
technology leveraged in Platform-as-a-Service (PaaS) offerings.
• Besides being an enabler for computation on demand, virtualization also gives the opportunity to
design more efficient computing systems by means of consolidation, which is performed transparently
to cloud computing service users.
• Since virtualization allows us to create isolated and controllable environments, it is possible to serve
these environments with the same resource without them interfering with each other.
• This opportunity is particularly attractive when resources are underutilized, because it allows
reducing the number of active resources by aggregating virtual machines over a smaller number of
resources that become fully utilized.
• This practice is also known as server consolidation, while the movement of virtual machine instances
is called virtual machine migration (see Figure 3.10).

• Because virtual machine instances are controllable environments, consolidation can be applied
with a minimum impact, either by temporarily stopping its execution and moving its data to
the new resources or by performing a finer control and moving the instance while it is running.
• This second techniques is known as live migration and in general is more complex to
implement but more efficient since there is no disruption of the activity of the virtual machine
instance.
• Server consolidation and virtual machine migration are principally used in the case of
hardware virtualization, even though they are also technically possible in the case of
programming language virtualization.
• Storage virtualization constitutes an interesting opportunity given by virtualization
technologies, often complementary to the execution of virtualization.
• Even in this case, vendors backed by large computing infrastructures featuring huge storage
facilities can harness these facilities into a virtual storage service, easily partitionable into
slices. These slices can be dynamic and offered as a service.
• Again, opportunities to secure and protect the hosting infrastructure are available, as are
methods for easy accountability of such services.
• Finally, cloud computing revamps the concept of desktop virtualization, initially introduced in
the mainframe era.
• The ability to recreate the entire computing stack—from infrastructure to application
services—on demand opens the path to having a complete virtual computer hosted on the
infrastructure of the provider and accessed by a thin client over a capable Internet connection.

Technology Examples:
• A wide range of virtualization technology is available especially for
virtualizing computing environments.
• The most relevant technologies and approaches utilized in the Cloud-
specific solutions are:
1) Xen: Paravirtualization
2) Vmware: Full Virtualization
3) Microsoft Hyper-V

Use this Link for Technology Examples:
• Click on the below link-
• https://slideplayer.com/slide/13501163/

1) Xen: Paravirtualization

2) VMware: Full Virtualization
I. Full Virtualization and Binary Traslation

II. Virtualization Solutions
a) End-User (Desktop) Virtualization

b) Server Virtualization(VMware GSX Server)

b) Server Virtualization(VMware GSXi Server)

c) Infrastructure Virtualization & Cloud-Computing Solutions

Migrating into a Cloud
1. The Promises of the Cloud
2. The Cloud Services Offerings and
Deployment Models
3. Challenges in the Cloud

1. The Promises of the Cloud

2. The Cloud Services Offerings and
Deployment Models

3. Challenges in the Cloud

• The Seven-Step Model of Migration Into a
Cloud

Unit 2 Virtualization Part I.pptx

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